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net: reduce RTNL hold duration in unregister_netdevice_many_notify() (part 1)

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Two synchronize_net() calls are currently done while holding RTNL.

This is source of RTNL contention in workloads adding and deleting
many network namespaces per second, because synchronize_rcu()
and synchronize_rcu_expedited() can use 60+ ms in some cases.

For cleanup_net() use, temporarily release RTNL
while calling the last synchronize_net().

This should be safe, because devices are no longer visible
to other threads at this point.

In any case, the new netdev_lock() / netdev_unlock()
infrastructure that we are adding should allow
to fix potential issues, with a combination
of a per-device mutex and dev->reg_state awareness.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jesse Brandeburg <jbrandeburg@cloudflare.com>
Link: https://patch.msgid.link/20250114205531.967841-5-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet 2025-01-14 20:55:30 +00:00 • committed by Jakub Kicinski
parent cfa579f666
commit ae646f1a0b
1 changed files with 3 additions and 0 deletions
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3
net/core/dev.c
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@ -11629,6 +11629,7 @@ void unregister_netdevice_many_notify(struct list_head *head,
rtnl_drop_if_cleanup_net(); rtnl_drop_if_cleanup_net();
flush_all_backlogs(); flush_all_backlogs();
rtnl_acquire_if_cleanup_net(); rtnl_acquire_if_cleanup_net();
/* TODO: move this before the prior rtnl_acquire_if_cleanup_net() */
synchronize_net(); synchronize_net();
list_for_each_entry(dev, head, unreg_list) { list_for_each_entry(dev, head, unreg_list) {
@ -11689,7 +11690,9 @@ void unregister_netdevice_many_notify(struct list_head *head,
#endif #endif
} }
rtnl_drop_if_cleanup_net();
synchronize_net(); synchronize_net();
rtnl_acquire_if_cleanup_net();
list_for_each_entry(dev, head, unreg_list) { list_for_each_entry(dev, head, unreg_list) {
netdev_put(dev, &dev->dev_registered_tracker); netdev_put(dev, &dev->dev_registered_tracker);